The present invention relates to a system for cooling engine oil in a vehicle such as a motorcycle. More particularly, the invention relates to an arrangement for controlling the flowability of oil discharged from a water-cooled oil cooler provided integrally with a crankcase of a vehicle engine.
In the prior art an oil cooling system employing water as the cooling fluid is described in Japanese Utility Model Laid-Open No. 56-105613 (No. 104513/1981). The described system is generally constituted such that engine oil is pumped from an oil pan by an oil pump which operatively connects to the engine crankshaft and is then passed to an oil filter and fed under pressure to an oil cooler mounted integrally with the engine. Engine oil so-fed to the oil cooler is thereafter supplied, after cooling to an appropriate temperature, to the several vehicle parts to be lubricated.
In such oil cooling device, engine oil, being at a low temperature when the engine is started, especially in cold regions, increases in viscosity, whereby the load on the oil pump is increased and the power requirements for driving the engine are increased. In the light of such a problem, it is an object of the present invention to provide a cooling system for cooling engine oil in which the oil inlet and outlet passages communicating with an oil cooler of the water cooled type are interconnected by a bypass flow passage containing an orifice, whereby, if the viscosity of the discharge oil from the cooler increases beyond an acceptable limit due to subjecting either the inlet oil or the cooling liquid to excessively low ambient temperatures and the pressure required to be produced by the oil pump to pump the oil is excessively increased, the viscosity of the engine oil can be regulated to remain within an acceptable range.
In order to attain the aforesaid object, the present invention provides a system for cooling engine oil in which a water-cooled oil cooler is provided integrally in the flow passage for engine oil connecting each of the engine parts to be lubricated with a storing portion for engine oil provided by the engine crankcase characterized in that a bypass flow passage is provided between the inlet and the outlet passages for the engine oil that communicate with the oil cooler so as to interconnect the two passages. Advantageously, the bypass flow passage may be provided with an orifice.